Regarding a conventional solid drawing material, its hardness is adjusted by optionally adding oils and resins to a blend of a wax, a pigment and a filler. However, when the amount of the oil is increased for the purpose of softening the solid drawing material, it breaks easily because of a decrease in its strength. In that case, it becomes impossible to form it into a thin shape, or to make its tip sharpened by cutting, and thus failing to perform fine drawing. Moreover, there is a problem that, when drawing on smooth non-absorbing surfaces of a coated paper, plastic, metal, glass, whiteboard and the like, it is impossible to draw darkly, regardless of its softness, because of slipping on the surfaces.
On the other hand, when the amount of the resin is increased so as to enhance its strength, it is possible to form it into a thin shape, but causes a problem that it is impossible to draw on smooth non-absorbing surfaces of a coated paper, plastic, metal, glass, whiteboard and the like because of its hardness.
For example, there is disclosed, as an unfired color pencil, the composition of a soft color lead having excellent colorability, containing a mixture of a glycerin fatty acid ester and/or pentaerythritol fatty acid ester each having a melting point of 65° C. or lower, rosin and/or a modified rosin (Patent Literature 1). The object of this patent literature is to obtain an oil painting-like work by dissolving the portion drawn on a canvas using oil for oil painting, and is different from the object of a solid drawing material of the present invention which is drawn on smooth non-absorbing surface of a coated paper, plastic, metal, glass whiteboard and the like.
There is also disclosed the composition of a solid drawing material which enables smooth drawing even on a non-absorbing drawing surface by containing, as a solid drawing material, a pigment, a wax and a mineral oil, and further containing a non-crystalline poly α-olefin and rosin in a given ratio (Patent Literature 2). However, it is required for this composition to contain 5% by weight or more of the mineral oil, and thus making it impossible to perform thin forming because of low strength. Actually, reference is not made to a diameter or the like of a molding even in Examples of the same literature.
By the way, in the chemical definition, wax refers to an “ester of fatty acid and a higher monohydric or dihydric alcohol”. In the definition, the wax also includes a wax which is liquid at normal temperature, like jojoba oil, for example, and a wax which is solid at normal temperature. However, usually, it may be considered that an “organic substance which is solid or semisolid at normal temperature”, and which is “melted at a temperature ranging from normal temperature to about 100° C., and has low melt viscosity” is collectively referred as a wax (Non-Patent Literature 1). Specifically, in addition to waxes according to the above chemical definition, esters of a trihydric (glycerin) or tetrahydric (pentaerythritol) alcohol belonging to the category of oils and fats and fatty acid, petroleum-based hydrocarbons such as paraffin wax, petrolatum, and microcrystalline wax, fatty acid alone and other substances are collectively referred to as the wax.
Of those collectively referred to as the “wax” mentioned above, most of those defined as “fatty acid and higher monohydric or dihydric alcohol” are inferior in compatibility with rosin, and modified rosin such as a glycerin ester of rosin.
To the contrary, an ester of trihydric (glycerin) or tetrahydric (pentaerythritol) alcohol and fatty acid has satisfactory compatibility with rosin, and modified rosin such as a glycerin ester of rosin.
As mentioned above, in the present invention, an “organic substance which is solid or semisolid at normal temperature”, and which is “melted at a temperature ranging from normal temperature to about 100° C., and has low melt viscosity”, especially an organic substance having a temperature at which it melts (a melting point) of 110° C. or lower is referred to as a “wax”.